/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.harmony.luni.util;

import java.lang.ref.SoftReference;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;

/**
 * The class extends the functionality of {@link java.lang.ThreadLocal} with
 * possibility of discarding the thread local storage content when a heap is
 * exhausted.
 */
public class ThreadLocalCache<T> {

	private SoftReference<ThreadLocal<T>> storage = new SoftReference<ThreadLocal<T>>(
			null);

	public static ThreadLocalCache<CharsetDecoder> utf8Decoder = new ThreadLocalCache<CharsetDecoder>() {
		@Override
		protected CharsetDecoder initialValue() {
			return Charset.forName("UTF-8").newDecoder();
		}
	};

	public static ThreadLocalCache<CharsetEncoder> utf8Encoder = new ThreadLocalCache<CharsetEncoder>() {
		@Override
		protected CharsetEncoder initialValue() {
			return Charset.forName("UTF-8").newEncoder();
		}
	};

	public static ThreadLocalCache<java.nio.ByteBuffer> byteBuffer = new ThreadLocalCache<java.nio.ByteBuffer>() {
		@Override
		protected java.nio.ByteBuffer initialValue() {
			return java.nio.ByteBuffer.allocate(72); // >=
			// Manifest.LINE_LENGTH_LIMIT
		}
	};

	public static ThreadLocalCache<CharBuffer> charBuffer = new ThreadLocalCache<CharBuffer>() {
		@Override
		protected CharBuffer initialValue() {
			return CharBuffer.allocate(72); // no specific requirement
		}
	};

	/**
	 * Returns the thread local value of this object.
	 */
	public T get() {
		return getThreadLocal().get();
	}

	private ThreadLocal<T> getThreadLocal() {
		ThreadLocal<T> tls = storage.get();
		if (tls == null) {
			tls = new ThreadLocal<T>() {
				@Override
				public T initialValue() {
					return ThreadLocalCache.this.initialValue();
				}
			};
			storage = new SoftReference<ThreadLocal<T>>(tls);
		}
		return tls;
	}

	/**
	 * Returns the initial value for the cache for the current thread.
	 */
	protected T initialValue() {
		return null;
	}

	/**
	 * Discards the cache for all threads.
	 */
	public void remove() {
		storage.clear();
	}

	/**
	 * Sets the value of this variable for the current thread. Might be useful
	 * for expanding the thread local cache.
	 */
	public void set(T value) {
		getThreadLocal().set(value);
	}

}
